Tokyo: Japanese Foreign Minister Katsuya Okada told his Chinese counterpart on Sunday that Tokyo would take "action" if China violates a 2008 agreement over disputed gas exploration projects.

In his talks with Yang Jiechi, Okada also urged China to start discussing details about jointly developing the gas projects in the East China Sea, said a Japanese diplomat, who declined to be named.

"If China violates the agreement, Japan will have to take certain action," Okada said in the talks, held on the sidelines of a meeting of foreign ministers from East Asia and Latin America.

Asia's two largest economies and top energy consumers in 2008 said they would share the potentially lucrative gas resources in the East China Sea, an agreement that was struck after years of negotiations.

But Japan has reportedly observed that China has built a drilling plant in the area and appears ready to start extracting gas.

In response, Yang told Okada: "China will firmly stand by the 2008 agreement. We wish to continue unofficial, working-level exchanges to further enhance mutual understanding."

China started drilling in Chunxiao gas field, known as "Shirakaba" in Japan, in 2003, inflaming tensions with Japan, which voiced worries that Beijing may siphon gas from the deposit that stretches into what Japan considered its own side.

The 2008 agreement stipulated that talks would continue over other gas fields, but China has since insisted that it has the right to develop them.